Abstract:

The invention relates to a joint part prosthesis, particularly for a
finger joint, consisting of either a proximal or a distal component, as
well as a shaft that extends away from this component, to be mounted in a
bone, which shaft is configured with a fin-like anti-twist device.
According to the invention, it is provided that as an anti-twist device
(7), at least two anti-twist elements (8) are disposed on the mantle
surface (6) of the shaft (4), with rotation symmetry, and extend radially
away from this mantle surface (6) and in the longitudinal direction of
the shaft (4), whereby the distance of the anti-twist elements (8) from
the mantle surface (6) decreases slightly in the direction toward the
free end (5) of the shaft (4).

Claims:

1-6. (canceled)

7. Joint part prosthesis, particularly for a finger joint, consisting of
either a proximal or a distal component, as well as a shaft that extends
away from this component, to be mounted in a bone, which shaft is
configured with a fin-like anti-twist device, wherein as an anti-twist
device (7), at least two anti-twist elements (8) are disposed on the
mantle surface (6) of the shaft (4), with, rotation symmetry, and extend
radially away from this mantle surface (6) and in the longitudinal
direction of the shaft (4), whereby the distance of the anti-twist
elements (8) from the mantle surface (6) decreases slightly in the
direction toward the free end (5) of the shaft (4).

8. Joint part prosthesis according to claim 7, wherein during insertion of
the shaft (4) into the medullary space of a bone, this space can be
cleared with the anti-twist device (7) and, at the same time, fixed in
place in it so as to prevent rotation.

9. Joint part prosthesis according to claim 7, wherein the anti-twist
elements (8) are configured to be thicker toward the shaft (4).

10. Joint part prosthesis according to claim 7, wherein the shaft (4) is
configured to be round in cross-section and spherical at its free end
(5).

11. Joint part prosthesis according to claim 7, wherein it is produced in
one piece, as a plastic injection-molded part.

Description:

TECHNICAL FIELD

[0001]The invention relates to a joint part prosthesis, particularly for a
finger joint. It consists of either a proximal or a distal component, as
well as a shaft that extends away from this component, to be mounted in a
bone.

STATE OF THE ART

[0002]Artificial finger joints consist essentially of two elements, namely
a proximal and a distal component. A component has a convex joint head
that interacts with the other part, which demonstrates a convex joint
socket.

[0003]Artificial finger joints are inserted between the metacarpal bone
and the finger bone, or between individual finger bones. Such joints have
to be inserted if degenerative joint diseases such as osteoarthritis,
post-traumatic arthritis, or rheumatoid arthritis of the joints in
question are present. Another alternative that retains mobility of the
individual finger members is a total joint replacement.

[0004]From the state of the art, particularly from EP 1203569 A (FINSBURY
(DEVELOPMENT) LIMITED LEATHERHEAD) Mar. 3, 2000, finger joint implants
are known in the configuration of so-called PIP shaft implants. They have
a proximal or a distal component, which components interact accordingly,
each having a shaft that points away from these components. The shaft is
generally configured to be conical and is introduced into the bone marrow
of a bone. In order to allow introduction, the interior of the bone is
partly cleared out using a clearing tool, and the implant is driven into
the bone using a hammer-like instrument. Fixation takes place in such a
manner that the diameter of the cleared bore is smaller than the outside
diameter of the shaft, so that a kind of press fit is formed between the
shaft and the interior of the bone.

[0005]The implant itself consists of a material having a modulus of
elasticity similar to bone. This modulus of elasticity similar to bone
avoids so-called stress shilding and thus promotes bone build-up.
Additionally, fixation of the implant in the medullary space of the bone
is improved in this manner.

DISADVANTAGES OF THE STATE OF THE ART

[0006]Products according to the state of the art have disadvantages such
as implant loosening due to insufficient fixation and insufficient
connection with the bone, as well as high wear values, thereby causing
corresponding friction wear. The shaft-like construction within the
medullary space creates sufficient room for itself if loosened, so that
an implant that was fixed in place previously is no longer functionally
correct. The consequences of this are pain caused by migration or even
fractures.

[0007]Furthermore, the disadvantage of the embodiments according to the
state of the art consists in that the individual joint part prostheses
cannot be disposed in a manner to reliably prevent twisting.

TASK OF THE INVENTION

[0008]It is therefore the task of the invention to further develop a joint
part prosthesis, particularly for finger joints, in such a manner that
the likelihood of loosening of the implant is reduced, in contrast to the
state of the art.

SOLUTION OF THE TASK

[0009]The core idea of the solution of the task is to provide the shaft
with wing-like or fin-like configurations, so that the rotation-symmetry
shape that is advantageous for production and for clearing out the
medullary space of the bone is retained, but nevertheless, an anti-twist
security device is provided.

[0010]One of the significant advantages of the invention is that because
of the configuration of the joint part prosthesis according to the
invention, it is no longer necessary to clear out the medullary space of
the bone into which the implant is to be placed by means of working on it
by hitting or hammering. Nevertheless, the joint part prosthesis can be
fixed in place in simple and efficient manner. Since the shaft of the
joint part prosthesis has rotation symmetry, it is sufficient to clear
out the medullary space of the bone by means of rotational movements. In
this way, damage to adjacent joints, in particular, caused by the
hammering process required for clearing, is avoided.

[0011]One of the other significant advantage of the invention is that the
joint part prosthesis can be inserted into the medullary space of a bone,
with its shaft, and is also fixed in place there, in anti-twist manner,
without additional steps being required.

[0012]The invention provides that anti-twist devices are provided on the
mantle surface of the shaft of the joint part prosthesis. An anti-twist
device comprises at least one fin-like element that is disposed on the
mantle surface of the shaft of the joint part prosthesis, and extends in
the longitudinal direction of the shaft. In this connection, it is
preferably narrow and advantageously configured to be somewhat thicker
toward the shaft. This brings with it the advantage that for one thing,
torques/torsions that occur can be absorbed by the anti-twist element.
For another thing, it has the advantage, because of the fact that the
free ends are configured to be narrower, that simple insertion into the
prepared cleared medullary space is possible.

[0013]A preferred embodiment of this anti-twist security device provides
that it/they increase in their reaches, proceeding from the free end, in
the direction of the distal or proximal component, so that twisting is
still possible at insertion of the implant, and the farther the implant
is introduced into the medullary space, the more likely it is that
twisting is configured to be restricted.

[0014]In order to be able to install such anti-twist devices together with
the shaft of a component, it is provided to clear the cavity accordingly.
Aside from the dimensions of the shaft, the spaces that project away
laterally are also cleared by means of a gauge, so that the implant can
be inserted with precise fit. Clearing preferably takes place by means of
rotating and oscillating movements, so that no hammering movements, which
put stress on the joints, are required.

[0015]In one exemplary embodiment, the joint part prosthesis consists of a
material that is known from the state of the art.

[0016]Preferably, the anti-twist elements form a one-piece part with the
shaft.

[0017]A preferred embodiment provides that the distance from the mantle
surface of the shaft decreases toward the free end of the anti-twist
element, in the direction of the free end of the shaft.

[0018]Another embodiment provides that the fin-like elements extend only
partly over the longitudinal expanse of the shaft. It is advantageous if
they are configured only in certain sections.

[0019]Alternatives provide that a plastic can be used, particularly in
order to achieve the modulus of elasticity similar to bone. This also
brings with it the particular advantage that the joint part prostheses
can be produced by means of injection-molding methods.

[0020]Other advantageous embodiments are evident from the following
description, the drawings, as well as the claims.

DRAWING

[0021]The drawing shows:

[0022]FIG. 1 a perspective view of the joint part prosthesis according to
the invention, with a proximal component, with an anti-twist security
device disposed on it.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

[0023]In FIG. 1, an embodiment of the embodiment of the invention
according to the invention is shown. The joint part prosthesis 1 shown
there consists comprises a proximal component 2, from which a shaft 4
extends to the rear. The shaft 4 extends almost perpendicular away from
the proximal component 2 and has a narrowing toward its free end 5 in the
exemplary embodiment shown here. It is configured to be round in
cross-section. The round cross-section brings with it the advantage that
this embodiment can be produced in simpler and more cost-advantageous
manner than an oval or rectangular shape, for example.

[0024]The free end 5 of the shaft 4 is preferably configured in ball-like
manner, so that no sharp edges can be formed, which can injure any marrow
of the bone during insertion of the prosthesis.

[0025]Furthermore, the wall of the shaft 4 is configured to be round,
particularly in the region of the free end 5.

[0026]On the mantle surface 6, the anti-twist device 7 according to the
invention is disposed. This anti-twist device 7 serves to fix a joint
part prosthesis 1 that has been introduced into a medullary space, which
space preferably takes up at least almost the same cross-section as the
shaft 4 configured together with the anti-twist device 7, in place in
such a manner that turning of the joint part prosthesis 1 within the
medullary space is no longer possible.

[0027]The anti-twist device 7 consists of at least one anti-twist element
8 that is configured in the longitudinal expanse of the shaft 4 and has a
fin-like construction.

[0028]Particularly in the region of the free end 5 of the shaft 4, it is
provided to configure the anti-twist element 8 very slightly, with regard
to its distance from the mantle surface of the shaft 4, so that during
introduction, corresponding positioning within the medullary space is
still possible. The deeper the joint part prosthesis 1 is introduced into
the medullary space, the more the fin-like anti-twist devices 7 penetrate
into the medullary space and press themselves into the marrow of the
bone. A corresponding wedge effect occurs.

[0029]The anti-twist element 7 prevents rotational movement of the joint
part prosthesis 1 in or opposite to the arrow direction 9. It serves at
least only slightly to bring about fixation of the joint part prosthesis
1 in the rotation direction, but also in the longitudinal direction.

[0030]The invention can be used for joint part prostheses in both the
distal or the proximal region. Likewise, use for all types of prostheses
that have a shaft-like configuration is possible, where it is important
to prevent a rotational movement of the joint part prostheses from being
possible.